Localization in Objective-C

Aug 20, 2012 objclocalization

This post will show you how to localize your iOS apps, so they can be translated to several languages. I’ll will describe how to translate plain text and how to create localized versions of your storyboards.

Since storyboard localization comes with a few quirks, let’s also discuss how to automate synchronizing changes that are made in storyboards.

Translating strings programmatically

Getting localization to work in iOS is pretty straightforward. You just have to do the following:

  • Add a new Localizable.Strings file to your project.

  • In the file, add your key-value-based translations, like this (each line has to end with a semi-colon):

"key_1" = "Translation 1";
"another key" = "Another translation";
  • To create a localized version of Localizable.Strings, select the file in the Project Navigator and add localizations in the File Inspector to the right.

  • When you have more than one version of this file, an arrow will appear next to the file in the Project Navigator.

  • Click the arrow to show all localized versions. Select any version in the list to modify that version.

Once you have your translations in place, use NSLocalizedString(key, ...) to translate keys:

NSLocalizedString("key_1", nil)

This will return “Translation 1” if English is currently used. If you switch to Swedish, the app would select the Swedish localization, if one exists. Any missing keys will default to the translation in the base file.

That’s really all there is to it. Before moving on, I just want to give you some advice.

First, do not use this approach to translate your storyboards. This requires a separate IBOutlet for each component that should be translated. If you just have a few controls to translate, fine, but please read on to find out how to do this in a better way.

Second, I want to advice against using translation key strings directly in code. Doing so makes your app vulnerable, since a translation will fail if a string is mistyped. These kinds of “bugs” are hard to find, since the Objective-C compiler will not detect incorrect strings.

Instead, add a file that contains a definition for each key, as well as a translation macro with only one parameter (for convenience). In my latest app, I call it AppStrings.h, and it looks something like this:

#define STR_CANCEL @"cancel"
#define STR_DELETE @"delete"
#define STR_OK @"ok"

#define Translate(key) \
[[NSBundle mainBundle] localizedStringForKey:(key) value:@"" table:nil]

As you see, this requires a little extra work, since you have to add a definition for each translation key. However, it gives you a clean interface, where keys strings are only used in this file. If a translation fails, this is the only place where it can be misspelled, since all other classes will use these definitions.

You can then use the Translate macro (or the native NSLocalizedString, even if it requires two parameters) together with any definition to translate your strings:


Translating storyboards

Translating text programmatically was really easy. Now, let’s see if translating storyboards is as simple.

You basically have (at least) two options:

  • Add an IBOutlet for each outlet that should be localizable, then translate it programmatically using the approach above.

  • Enable localization for your Storyboard and add a separate storyboard variant for each language you have to support.

As I wrote above, don’t use the first option if you have a lot of localized components in your storyboard. It will result in a lot of outlets. Instead, I suggest that you enable localization by doing the following:

  • Select your Storyboard in the Project Navigator

  • To create a localized version of the file, select it in the Project Navigator and add localizations in the File Inspector to the right.

  • When you have more than one version of this file, an arrow will appear next to the file in the Project Navigator.

  • Click the arrow to show all localized versions of the storyboard.

You can now edit any version of the storyboard drectly. Translate texts, replace icons etc. That’s it - simple, eh? Well, not really. Once you have your versions set up, you will bump into this:

  • You have an original storyboard.

  • You create a localized version of the storyboard.

  • You make changes to the original storyboard, such as adding or removing something.

  • BOOOOM! The changes will not be made to the localized version of the storyboard.

Since Xcode doesn’t keep the storyboards in sync, localizing early will result in tremendous amount of extra work. Each change has to be done in each localized version…and that is just baaaaad.

Luckily, I found this great Python script that keeps your storyboards in sync:

Watch the video to find out how to make the script keep all storyboards in sync each time the project is built. If you don’t have five minutes to spare, you can download the script here and add the following as a build step:

python [path to the python script] --mainIdiom=[the main idiom] --mainStoryboard=[path to the main storyboard] [list of idioms to translate]


To wrap up, localization is easy, but storyboards can mess up your workflow when you change a lot in the storyboards. I usually stick to localizing buttons, labels etc. with code instead.